Glucokinase (GK) is one of four hexokinases found in mammals [Colowick, S. P., in The Enzymes, Vol. 9 (P. Boyer, ed.) Academic Press, New York, N.Y., pages 1-48, 1973]. The hexokinases catalyze the first step in the metabolism of glucose, i.e., the conversion of glucose to glucose-6-phosphate. Glucokinase has a limited cellular distribution, being found principally in pancreatic xcex2-cells and liver parenchymal cells. In addition, GK is a rate-controlling enzyme for glucose metabolism in these two cell types that are known to play critical roles in whole-body glucose homeostasis [Chipkin, S. R., Kelly, K. L., and Ruderman, N. B. in Joslin""s Diabetes (C. R. Khan and G. C. Wier, eds.), Lea and Febiger, Philadelphia, Pa., pages 97-115, 1994]. The concentration of glucose at which GK demonstrates half-maximal activity is approximately 8 mM. The other three hexokinases are saturated with glucose at much lower concentrations ( less than 1 mM). Therefore, the flux of glucose through the GK pathway rises as the concentration of glucose in the blood increases from fasting (5 mM) to postprandial (≈10-15 mM) levels following a carbohydrate-containing meal [Printz, R. G., Magnuson, M. A., and Granner, D. K. in Ann. Rev. Nutrition Vol. 13 (R. E. Olson, D. M. Bier, and D. B. McCormick, eds.), Annual Review, Inc., Palo Alto, Calif., pages 463-496, 1993]. These findings contributed over a decade ago to the hypothesis that GK functions as a glucose sensor in xcex2-cells and hepatocytes (Meglasson, M. D. and Matschinsky, F. M. Amer. J. Physiol. 246, E1-E13, 1984). In recent years, studies in transgenic animals have confirmed that GK does indeed play a critical role in whole-body glucose homeostasis. Animals that do not express GK die within days of birth with severe diabetes while animals overexpressing GK have improved glucose tolerance (Grupe, A., Hultgren, B., Ryan, A. et al., Cell 83, 69-78, 1995; Ferrie, T., Riu, E., Bosch, F. et al., FASEB J., 10, 1213-1218, 1996). An increase in glucose exposure is coupled through GK in xcex2-cells to increased insulin secretion and in hepatocytes to increased glycogen deposition and perhaps decreased glucose production.
The finding that type II maturity-onset diabetes of the young (MODY-2) is caused by loss of function mutations in the GK gene suggests that GK also functions as a glucose sensor in humans (Liang, Y., Kesavan, P., Wang, L. et al., Biochem. J. 309, 167-173, 1995). Additional evidence supporting an important role for GK in the regulation of glucose metabolism in humans was provided by the identification of patients that express a mutant form of GK with increased enzymatic activity. These patients exhibit a fasting hypoglycemia associated with an inappropriately elevated level of plasma insulin (Glaser, B., Kesavan, P., Heyman, M. et al., New England J. Med. 338, 226-230, 1998). While mutations of the GK gene are not found in the majority of patients with type II diabetes, compounds that activate GK and, thereby, increase the sensitivity of the GK sensor system will still be useful in the treatment of the hyperglycemia characteristic of all type II diabetes. Glucokinase activators will increase the flux of glucose metabolism in xcex2-cells and hepatocytes, which will be coupled to increased insulin secretion. Such agents would be useful for treating type II diabetes.
This invention provides a compound, comprising a substituted hydantoin of the formula: 
wherein
R1 is a five- or six-membered aromatic heterocyclic ring having one to three heteroatoms selected from nitrogen, oxygen, and sulfur, which ring is unsubstituted or substituted with halo, amino, hydroxylamino, nitro, cyano, sulfonamido, lower alkyl, perfluoro lower alkyl, lower alkyl thio, perfluoro-lower alkyl thio, lower alkyl sulfonyl, perfluoro-lower alkyl sulfonyl, lower alkyl sulfinyl, or xe2x80x94(R5)nxe2x80x94C(O)xe2x80x94OR6;
R2 is a cycloalkyl ring containing from 5 to 7 carbon atoms;
R3 is hydrogen, lower alkyl, a cycloalkyl ring containing from 5 to 7 carbon atoms, unsubstituted aryl, aryl substituted with halo or hydroxy, or an unsubstituted five- or six-membered aromatic heterocyclic ring having one or two heteroatoms selected from nitrogen, oxygen, and sulfur;
R4 is hydrogen, lower alkyl, or R3 and R4 together with the carbon atom to which they are attached form a cycloalkyl ring containing 5 to 7 carbon atoms;
R5 is xe2x80x94C(O)xe2x80x94 or lower alkyl;
R6 is lower alkyl;
n is 0 or 1; * and ** each designate an asymmetric centers,
and pharmaceutically acceptable salts thereof.
The compounds of Formula I have been found to activate glucokinase. Glucokinase activators are useful for increasing insulin secretion in the treatment of type II diabetes. Therefore compounds of this invention are useful to increase insulin secretion in view of their activity as glucokinase activators.